In a manufacturing process of a semiconductor device, various films having different physical properties are formed on a silicon substrate and these films are subjected to various processes, thus forming fine metal interconnects. For example, in a damascene interconnect forming process, interconnect trenches are formed in a film, and the interconnect trenches are then filled with metal, such as Cu. Thereafter, an excessive metal is removed by chemical mechanical polishing (CMP), so that metal interconnects are formed. After polishing of a substrate, the substrate is usually cleaned by a substrate cleaning apparatus. The substrate is cleaned by rotating the substrate horizontally and rubbing a roll cleaning tool, such as a roll sponge, against the substrate while supplying a cleaning liquid, such as chemical liquid, from a supply nozzle onto the substrate.
When the substrate is scrub-cleaned with the roll cleaning tool in the presence of the cleaning liquid, cleaning debris, such as particles, is generated. As a result, the cleaning liquid containing the cleaning debris is present on the substrate. It is preferable to remove such cleaning liquid from the substrate as quickly as possible. However, since the substrate is rotated horizontally, it takes a certain amount of time to remove the cleaning liquid from the substrate by a centrifugal force. As the substrate is rotated, the cleaning liquid on the substrate is brought into contact with the roll cleaning tool again and is then pushed back toward a central side of the substrate by a fresh cleaning liquid supplied from the supply nozzle. As a result, the cleaning liquid containing the cleaning debris remains on the substrate for a long time and dilutes the fresh cleaning liquid that has been supplied to the substrate, thus lowering a cleaning efficiency.
As a conventional substrate cleaning apparatus, there has been known an apparatus for cleaning a substrate by bringing a roll sponge into contact with a surface of the substrate while rotating the substrate in a vertical position. FIG. 14 is a schematic side view showing a conventional substrate cleaning apparatus, and FIG. 15 is a front view of the substrate cleaning apparatus shown in FIG. 14. As shown in FIGS. 14 and 15, the substrate cleaning apparatus includes two rollers 101, 102 for supporting and rotating a substrate W in a vertical position, two roll sponges 104, 105 that contact both surfaces of the substrate W supported by the rollers 101, 102, and cleaning-liquid supply nozzles 106, 107, 108 for supplying cleaning liquid onto the both surfaces of the substrate W.
The substrate W is cleaned as follows. The substrate W is rotated by the two rollers 101, 102, while the roll sponges 104, 105 are rotated about their axes. In this state, the cleaning liquid is supplied onto the substrate W from above the roll sponges 104, 105. The both surfaces of the substrate W are scrub-cleaned with the roll sponges 104, 105 in the presence of the cleaning liquid.
In the conventional apparatus shown in FIGS. 14 and 15, the roll sponges 104, 105 are rotated in respective directions such that the substrate W is pushed downward, and the two rollers 101, 102 support a downward load of the substrate W. However, such a configuration has the following drawbacks. The surfaces of the substrate W are cleaned by the sliding contact between the roll sponges 104, 105 and the substrate W in the presence of the cleaning liquid. Therefore, a region where the highest cleaning effect is achieved on the surface of the substrate W is a region C where a relative velocity between the roll sponges 104, 105 and the substrate W is maximized.
The cleaning liquid existing on the region C is brought into contact with the roll sponges 104, 105 again at a region D as the substrate W is rotated. The cleaning liquid that has been used in cleaning of the substrate W at the region C contains the cleaning debris, such as particles. Therefore, when the cleaning liquid that has once been used in cleaning of the substrate is again brought into contact with the roll sponges 104, 105 at the region D, the cleaning debris may be attached to the roll sponges 104, 105. Moreover, the cleaning liquid containing the cleaning debris is pushed back inwardly on the substrate W by a fresh cleaning liquid supplied from the outside of the substrate W, and is therefore unlikely to be removed from the substrate W. Consequently, the used cleaning liquid may dilute the fresh cleaning liquid, resulting in a lowered cleaning effect.